Hi Dean,
A serial # 63xxx would certainly be well into the "brown" plastic...
From the info. presented in V. Bobba's book and a few other books, here is the color vs. serial number ranges (Please note the cut-over dates and/or serial numbers are not firm and some overlap occurs) :
# 50001 to # 57000 - Red plastic in years 1933-39
# 57000 to # 65000 - Brown plastic in years 1939-42
# 65000 to end (~ # 77941) - Black plastic in years 1942-46
In the commercial range (i.e. P25xxx series) :
# P25000 to # P25300 - Red plastic
# P25301 to # P25800 - Brown plastic
# P25801 to # P26600 and # P77941 to # P78258 - Black plastic
Regards,
Pete... <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />